1. Field of the Invention
This invention relates to an illumination apparatus used for a cellular analysis apparatus such as a microscope, and more specifically, to an illumination apparatus provided with light sources for irradiating a cell or nucleus labeled by fluorescence with excitation light.
2. Description of Related Art
Conventional illumination apparatuses have long been applied to general illumination, decoration, advertisement, warning, introduction, and illumination for amusement. Such illumination apparatuses are available with light sources of types, such as filament lamps, halogen lamps, xenon lamps, mercury lamps, mercury xenon lamps, and fluorescent lamps, or with various light sources which are not limited to these types. These light sources, when used in the illumination apparatus for the cellular analysis apparatus, have the following many disadvantages.
For example, the light source, such as a halogen lamp or filament lamp, generates undesirable heat for maintaining a state of a cell and light produced by this light source is limited to white or yellow light. Hence, the illumination apparatus using such light sources requires lenses and filtering systems in considerable numbers in order to produce light of various wavelengths (colors) as excitation light used for the analysis of the cell. As a result, time during which a desirable state for the observation of the cell can be maintained is appreciably reduced and cost is materially increased. Further, each of the conventional light sources mentioned above has highly limited product life, which is about 2000 hours. Still further, in the ambiance that is exceedingly subject to shock and vibration, the light source is liable to be damaged.
However, light-emitting diode (LED) light sources have made great strides in recent years and are the ones that have high return on investment, replacing the conventional light sources. The LED light source, in contrast with the conventional light source, has distinct advantages that the product life of most light sources is as long as ten thousand hours or more and in addition, the consumption of electric energy relative to the intensity of given light is low. Moreover, the LED light source also has advantages that durability relative to shock and vibration is high, a heat loss is small, response time for switching is very short, and the selection of illumination color is wide.
For a conventional illumination apparatus in which the LED light source is used in the cellular analysis apparatus such as the microscope, for example, Japanese Patent Kokai No. 2005-321453 discloses an illumination apparatus in which the light source is constructed with a plurality of light-emitting diodes emitting light of different wave-lengths so that light from the plurality of light-emitting diodes is introduced into a common optical path. This illumination apparatus is such that the amount of light of each of the light-emitting diodes can be adjusted through the operation of an operation section.
In the observation and analysis of the cell, it is required that changes of the location, shape, and intensity of fluorescent light of a substance for its object are quantitatively found from an image, and thus it is essential that the amount of light of each of illumination light sources used for the observation and analysis of the cell is kept constantly from the start of the observation to the end.
However, the LED light source has the drawback that although the LED light source is smaller in heat loss than other light sources, its amount of light is changed because of the influence of heat generated from the ambience of the LED light source and the LED light source itself. In addition, due to the deterioration of the LED light source itself, the change of the amount of light may be brought about.
Also, as the conventional light source other than the LED light source, for example, in a microscope using a plurality of laser light sources, there is a light source which has a detection means for detecting the amount of laser light and a light-adjusting means for adjusting the amount of laser light in accordance with the amount of light obtained by the detection means (refer to, for example, Japanese Patent Kokai No. 2005-235954). This microscope is constructed so that light from the laser light sources is split into two optical paths, one of which is directed toward a specimen and the other is directed toward the detection means, through a beam splitter placed on the optical axis and the amount of light directed toward the detection means is detected.